Gone Swimming

The fastest way to cool off in the summer time is to go for a swim. And while you're lounging on your neon pink floaty, you're probably not thinking about the acidy level of the pool (then again, this is an engineering community), but it is a critical component of the health and safety of you and your swimming mates.

Image Credit:bassethoundtown.com

In order to check and maintain a safe level of chlorine, you can use anoxidation reduction potential (ORP) instrument, also known as redox potential instruments. The devices are primarily used to monitor chemical reactions. ORP instruments measure the ability of a solution to act as an oxidizing agent, and to quantify ion activity. It is a rugged electrochemical test, which is convenient and easy to use.

ORPs measure the oxidizing ability of chlorine in swimming pools and spas, and determine when the equivalence point has been reached in an oxidation-reduction reaction. ORP instruments are also used for cooling tower disinfection, groundwater remediation, bleaching, cyanide destruction, chrome reductions, metal etching, fruit and vegetable disinfection, and dechlorination.

Chemicals like chlorine, bromine, and ozone are all strong oxidizers. Because they are able to take electrons from other substances they are excellent sanitizers (they kill said pool mates' foot funk). The act of sanitization is caused by the alteration of the chemical makeup of the unwanted organism, their ability to oxidize is reduced until they are used up or combined with another substance. The oxidation process can be monitored by an ORP instrument and the user can identify the end of the sanitization process. Oxidation reduction potential instruments can possibly select an individual ORP value, expressed in millivolts, at which a predictable level of disinfection can be achieved and sustained regardless of variations in either oxidant demand or oxidant concentration.

ORP water source field test. Image Credit: Wittenberg University

Oxidation reduction potential instruments have proven their use as analytical tools in monitoring changes in a system rather than determining their absolute value (e.g., process control and titrations).

Oxidation Reduction Reactions

Oxidation reduction potential is a measurement of the electrical potential of a redox reaction. It also serves as a measure of how much oxidation or reduction takes place in the given conditions. Redox reaction refers to the exchange of electrons. I'm sure you guys learned all about this in Chemistry 101. Although there is no shame in forgetting and I won't tell if you click this link to jog your memory. The ORP measurement is not a measurement of concentration; rather it measures the activity level, similar to a pH test. The basic thermodynamics for ORP reactions can be expressed using the Nerest equation. The general process for performingan oxidation reduction potential test consists of six steps described in the image below.

Image Credit: HACH

When selecting an oxidation reduction potential instrument there are several important factors to consider. They are described in the video here.

As seen in the chart below, reactions produce a positive or negative ORP depending on the type and quality of the occurring reaction. The oxidation scale can go from about -1000 to +1000. Sources with a strong negative ORP are safer to consume.